Our Solar System Is a Rare Gem

As if in time for the upcoming film release of The Privileged Planet (see 06/24/2004 headline), Philip Ball wrote a line for Nature Science Update that would have dismayed Carl Sagan and a host of SETI researchers: “Earth-like planets may be more rare than thought… In cosmic terms, our solar system could be special after all.”  The opinion is coming from research on extrasolar planets that suggests they were formed by a different process than what formed ours.  If that is so, according to Martin Beer, our solar system may be highly unusual and “there won’t necessarily be lots of other Earths up there.”  Ball comments,

Ever since Copernicus displaced the Earth from the centre of the Universe, astronomers have tended to assume that there is nothing special about our place in the cosmos.  But apparently our planetary system might not be so normal after all.  Is it just chance that makes Jupiter different from other extrasolar planets?  Beer and his colleagues suspect not.

Ball suggests that our solar system was formed by accretion of planetesimals, whereas the extrasolar planets seen so far were formed by a rapid disk instability process.  The observations show 110 Jupiter-class objects with wildly eccentric orbits or orbits too close to the star; in either case, rocky planets in the habitable zone could not exist.  In contrast, our Jupiter is far from the sun, and both Earth and Jupiter have nearly circular orbits.  More observations will be required to discern whether there really are two methods for making solar systems, and for determining “how unusual we really are.”
    An article on Astrobiology Magazine makes a similar statement.  “On the evidence to date, our solar system could be fundamentally different from the majority of planetary systems around stars because it formed in a different way.  If that is the case, Earth-like planets will be very rare.”  Space.Com has a similar report.

It was common for magazine and newspaper articles in the Sagan era to claim as matters of fact, “We are nothing special,” and to drone in weary prose set to timeless Vangelis music about how we are lost in space, drifting aimlessly on a tiny speck of insignificant dust in a vast, uncaring universe.  The data so far are not supporting that point of view.  Also, to set the record straight, Copernicus did not displace Earth from the center of the universe, because medieval cosmologists never put it there to begin with (see 06/24/2004 headline).
    It’s refreshing to see Philip Ball and some others starting to change their tone and recognize the extraordinary congruence of improbable factors that make our planet beautiful.  Next step is to help them cure their bad habit of talking like eyewitness news reporters, and treating speculative theories as historical facts.  Most of the following fairy tale from the NSU article, for instance, is built on imagination, not fact:

The planets in our Solar System were put together from small pieces.  The cloud of gas and dust that surrounded our newly formed Sun agglomerated into little pebbles, which then collided and stuck together to form rocky boulders and eventually mini-planets, called planetesimals.  The coalescence of planetesimals created rocky planets such as Earth and Mars, and the solid cores of giant planets such as Jupiter, which then attracted thick atmospheres of gas.

Recent observations are showing that stars blast away their dust disks in short order, far too rapidly for the formation of planets, even if the rest of the fairy tale were true.  But then, small bits of dust and rock do not stick together; they bounce.  What’s more, it takes a pretty large body to have enough gravity to start attracting material around it, and then it has to stop attracting material in time to avoid being dragged into the star.  So there are multiple improbabilities in getting a solar system to form.  Even the showcase of planetary evolution, Tau Ceti, is now looking too hostile to be considered a planet garden (see 07/06/2004 headline).  If you don’t accept the Design viewpoint, you have to thank your lucky star: the sun.